This is a xc2xa7371 of International Application No. PCT/BE00/00020, with an international filing date of Mar. 1, 2000, which is based on European Patent Application No. EP 99201121.3, filed Apr. 13, 1999.
The present invention relates to a method for measuring respective positions of a set of N contact elements of an electronic component.
According to the state of the art, the contact elements of the electronic component are illuminated by means of alight source and a camera is used to record an image of the contact elements. The positions of each of the contact elements are determined by using the recorded picture. The determination of these positions is important for the computation of the coplanarity of contact elements of electronic components such as BGA (Ball Grid Array)/CSP (Chip Scale Packaging) and flip-chip devices. If that coplanarity is not within predetermined and limited constraints, the necessary electrical contacts can not be made and the electronic component is useless.
It would therefore be advantageous to provide a method for measuring positions of a set of contact elements of an electronic component, without moving either the camera or the light source.
For this purpose a method according to the invention comprises:
bringing said set of elements in a measurement plane;
illuminating said measurement plane by means of a substantially homogeneous light source producing a light with an incident angle on said elements of at the most 20xc2x0;
recording a first image of said elements by means of a first camera having a first image plane extending substantially in parallel with said measurement plane;
recording a second image of said elements by means of a second camera set up over a triangulation angle xcex1 with respect to said first camera and said measurement plane, said triangulation angle being situated between 25xc2x0 and 80xc2x0;
determining within said first image for each ith (1xe2x89xa6ixe2x89xa6N) element, a first image point X1 of a first reference point situated on each of said elements;
determining within said second image a second image point X3 by mapping with respect to a calibration plane each time said first image point X1 into said second image;
determining with said second image, a third image point X4 being the image of said first reference point;
determining within said first image a fourth image point X2 by mapping said third image point into said first image;
determining within said first image a displacement xcex94xi between said first and fourth image point.
The first image enables to determine the X and Y position whereas the second image, in combination with the first, enables to determine the Z position or height Since two cameras are used, it is no longer necessary to move the light source or the camera. Since the two cameras are set up according to a triangulation angle with respect to each other, some distortion occurs in the second image recorded by the camera. This is however mathematically corrected as the angle is known between the two cameras. The use of a light source producing a light with an incident angle of at the most 20xc2x0 enables to illuminate the component with a same light source for both cameras.
A first preferred embodiment of a method according to the present invention is characterised in that said first X1 and third image point X4 are determined by means of a convolution operation with a predetermined convolution pattern. The use of a convolution pattern enables an easy and reliable subpixel calculation based on the grey values of the pixels in the recorded first and second image.
A second preferred embodiment of a method according to the present invention is characterised in that said convolution pattern is a circle for said first image, and an ellipse shaped curve for said second image. Those convolution patterns fit with the images recorded when the triangulation angle is approximately 45xc2x0.
A third preferred embodiment of a method according to the present invention is characterised in that said reference point is situated offset of a top of said element. With the incident light and the chosen triangulation angle the top of the element can not be reached exactly. Therefore, a point offset with respect to the top Is considered. However as this is done for all the elements and as only the relative position is of importance, this choice fits with the chosen methodology.
The invention also relates to an apparatus for measuring respective positions of a set of contact elements of an electronic component.